The Collaborative International Dictionary of English v.0.48:

Birthwort \Birth"wort`\, n.
   A genus of herbs and shrubs (Aristolochia), reputed to have
   medicinal properties.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Aristolochia
    n 1: birthworts; Dutchman's-pipe [syn: Aristolochia, genus
         Aristolochia]